URANIUM AND NEPTUNIUM IN BOROSILICATE GLASS: THE INFLUENCE OF THE MELTING CONDITIONS.

Neptunium- or uranium-doped borosilicate glasses have been prepared by melting of SiO//2, Na//2CO//3, Na//2B//4O//7 and AnO//2 (or U//3O//8) powder mixtures (An is uranium or neptunium). The influence of the melting conditions was studied and various crucibles were used for heating under different oxidizing conditions. The distribution between the different states of oxidation for the actinides in the glass matrix has been analyzed by optical spectroscopy and confirmed by Mossbauer spectroscopy. The valencies of uranium and neptunium were found to be U**4** plus , U**5** plus , U**6** plus , and Np**3** plus , Np**4**+30,depending on the state of oxidation of the actinide added to the mixture before melting, the composition of the glass matrix, the amount of actinide (less than 5 wt. %), the time and temperature of melting and the furnace atmosphere.